Personal System/2 Model 55 SX

A PS/2 Model 55 SX
Developer	International Business Machines Corporation (IBM)
Manufacturer	IBM
Product family	Personal System/2
Type	Personal computer
Release date	May 9, 1989; 36 years ago (1989-05-09) (Model 55 SX) October 9, 1990 (Model 55 SL)
Lifespan	1989–1992
Discontinued	May 1992 (1992-05)
Units sold	Over 1 million
Media	1.44 MB 3.5-in floppy disks (Model 55 SX) None (Model 55 SL)
CPU	Intel 386SX at 16 MHz
Storage	30–80 MB hard drive (Model 55 SX) None (Model 55 SL)
Graphics	Video Graphics Array
Power	120/240 VAC ～
Successor	PS/2 Model 57 PS/2 Model 56 PS/2 Model 53 486SLC2
Related	List of IBM PS/2 models

ThePersonal System/2 Model 55 SX is a midrange desktop computer inIBM'sPersonal System/2 (PS/2) family of personal computers. First released in May 1989, the Model 55 SX features anIntel 386SX processor running at aclock speed of 16 MHz. In October 1990, IBM introduced adiskless workstation version of the Model 55 SX, called thePersonal System/2 Model 55 LS. The Model 55 SX was the best-ever selling computer in the PS/2 range, accounting for 23 percent of IBM's PC sales within four months of its introduction. By 1991, the PS/2 Model 55 SX was the best-sellingx86-based PC in the world.^[1]

IBM succeeded the Model 55 SX with thePersonal System/2 Model 57 in 1991, thePersonal System/2 Model 56 in 1992, and thePersonal System/2 Model 53 SLC2 subfamilies in 1993, with IBM discontinuing the Model 55 SX in mid-1992.

IBM announced the PS/2 Model 55 SX on May 9, 1989, alongside theportablePS/2 Model P70. The Model 55 SX was IBM's first personal computer to use the386SX processor byIntel, released almost a year earlier in June 1988.^[2][3] The 386SX was a cost-reduced version of the 32-bit386 processor, also by Intel. Internally, the 386SX supports 32-bit operations, but its data bus could only access RAM 16 bits at a time, leading to a performance reduction of around 30 percent compared to a 386 processor with the sameclock speed.^[3] The PS/2 Model 55 SX sports a horizontal desktop case exactly identical to that of thePS/2 Model 30, released earlier in 1987.^[2]

The Model 55 SX, along with the Model P70, were the first new models of PS/2 to be assembled from the beginning at IBM's factory inRaleigh, North Carolina. Previously, models of PS/2 were manufactured at IBM's facility inBoca Raton, Florida, before the company moved personal computer production to Raleigh in 1989. Prototyping of the computers were still performed in Boca Raton, however.^[4] Owing to initial runs of the 55 SX's motherboard failing to meet IBM's quality-control standards, announcement of the computer was delayed by over a month, according toInfoWorld, pending motherboard design revisions.^[5]: 1

All models of the Model 55 SX features a 386SX processor clocked at 16 MHz and have 2 MB ofRAM stock and on-boardVGA graphics.^[2][6][7] As a consequence of the processor's 16-bit data path, the Model 55 SX sports only three 16-bit Micro Channelexpansion slots, whereas other true 32-bit offerings in the PS/2 line carried at least some 32-bit slots.^[2] One of the Model 55 SX's 16-bit slots features an extension for specific MCAgraphics adapters such as the8514/A.^[8]: 36 The initial two models in the PS/2 Model 55 SX range were the Model 55 SX-031, featuring a 30-MBhard disk drive, and the Model 55 SX-061, featuring a 60-MB hard drive.^[2] In June 1991, IBM introduced two more models of Model 55 SX, with 40- and 80-MB drives (the Model 55 SX-041 and Model 55 SX-081, respectively).^[7] All hard drives were ofEnhanced Small Disk Interface (ESDI) specification, which IBM used extensively in the PS/2 range and which was faster than theST-506 interface of older IBM PCs.^[9] The computer has two 3.5-inchdrive bays, both occupied as stock by the included hard drives and the3.5-inchfloppy disk drives. Users had to make use of external drives if they wanted more storage options, with the associated controllers taking up one of the three Micro Channel slots.^[10]

On October 9, 1990, IBM introduced the Model 55 LS (LAN Station), which werediskless-workstation versions of the Model 55 SX featuring no installed drives—not even a floppy drive. Instead, the computers came preinstalled with either anEthernet adapter or aToken Ring adapter (IBM's own networking standard), with the machinesbooting their operating system from a LAN server and having all applications and data remotely served and saved. IBM had been offering the Model 55 LS as a special bid version of the Model 55 SX for customers who specifically requested since its release in 1989, but the Model 55 LS was IBM's first computer specifically branded as a diskless workstation.^[6]

Sales of the Model 55 SX ramped up significantly over the summer of 1989, with the machine representing 23 percent of all IBM personal computers sold by September 1989, up from 4 percent only two months earlier.^[11] This share of IBM's PC sales remained steady into the next year, the Model 55 SX representing 22 percent of IBM's PC sales in June 1990.^[12] For the majority of 1990, it was the best-selling personal computer in the United States.^[13] By 1991, it was the best sellingx86-based PC globally.^[1] It was IBM's best-selling PS/2 by a significant margin, with the company selling 25,000 units of the computer in August 1990 alone.^[6] The heretofore best-sellingPS/2 Model 50 Z, meanwhile, sold only 18,000 in a single month (October 1988).^[14] This represented a reversal of fortunes for the PS/2 line, which had underperformed as a whole compared to IBM's earlier PC line.^[1] The Model 55 SX proved so popular that IBM reported parts shortages in April 1990.^[15]

Apple Computer eventually overtook IBM for the number one spot in U.S. computer sales with theMacintosh Classic in June 1991.^[16] However, it retained its status as the best-selling PC-compatible computer for the remainder of 1991 and the first half of 1992.^[1][17][18] IBM officially withdrew the PS/2 Model 55 SX in May 1992, replacing it with the similarly specced PS/2 Models 56 and 57.^[19] In December 1993, IBM brought out the PS/2 Model 53 SLC2, which sported an almost identical case to the 55 SX but replaced the motherboard with one manufactured byReply Corporation featuring theIBM 486SLC2 processor, clocked at 50 MHz.^[20]

Despite its massive sales success, the Model 55 SX received mixed, generally negative, reviews in the press. Although the computer earned an Editors' Choice Award inPC Magazine in 1990,^[21] the magazine's Tom Unger had earlier wrote that, "Even with the loaded motherboard, some users may feel constrained by getting just three expansion slots", praising the solid construction and motherboard integration while panning the hard drive for being slow.^[10]: 136InfoWorld's Eugene Wong called the Model 55 SX slower than most other 16-MHz 386SX machines despite being significantly more expensive.^[22] Russ Lockwood ofPersonal Computing found it the slowest of four 386SX machines reviewed and wrote that the Micro Channel architecture's potential forbus mastering was wasted on the drive controller and on-board graphics which were not capable of such. However, unlike Wong, he praised the motherboard's construction and called it price-competitive.^[23] In a review of several 386SX machines,PC World's T. J. Byers put it at the bottom of the list owing to its slow performance and limited potential for expansion.^[24]

IBM succeeded the Model 55 SX with the PS/2 Model 57 in 1991, the PS/2 Model 56 in 1992, and the PS/2 Model 53 SLC2 subfamilies in 1993. Each featured faster and more advanced microprocessors and, barring the Model 53 SLC2, redesigned cases. Neither three sold nearly as well as the PS/2 Model 55 SX;^[28][29] by late 1993,PC Week described the PS/2 line "beleaguered" as a whole due to diminishing market share and IBM's reputation for constant delays caused by parts shortages.^[28]

The PS/2 Model 57 was introduced by IBM in June 1991 as an upgrade to the PS/2 Model 55 SX; both were sold concurrently. The originalPS/2 Model 57 SX features a 20-MHz 386SX processor, 25 percent faster than the 55 SX's own 386SX processor. In addition, it sports a much larger case than the Model 55 SX, accommodating two additional 16-bit Micro Channel expansion slots and two more drive bays. The Model 57 SX also increases the base amount of RAM to 4 MB, expandable to 16 MB. It was the first PS/2 model to come equipped with 2.88-MB, 3.5-inch "super" floppy disk drives manufactured byToshiba.^[30][31] In October 1991, IBM introduced amultimedia PC version of the PS/2 Model 57 called thePS/2 Ultimedia M57 SLC. It features IBM's own manufactured microprocessor, theIBM 386SLC—a licensed clone ofIntel's 386SX clocked at 20 MHz. IBM claimed a 88 percent increase in performance over Intel's 386SX at the same clock speed. As a multimedia PC, IBM included with the Ultimedia M57 SLC aCD-ROM XA drive; anXGA graphics adapter; a 16-bitsound card, the M-Audio Capture and Playback Adapter/A (M-ACPA); aSCSI host adapter for controlling up to sevenSCSI devices; and front-mounted audio controls and speaker and headphone jacks.^[32][33]

In September 1992, after the Model 55 SX's discontinuation, IBM followed up the Model 57 SX with thePS/2 Model 57 486SLC2, featuring the 50-MHzIBM 486SLC2 processor. The 486SLC2 is a clock-doubled version of IBM's earlier 486SLC processor—itself a revamp of the IBM 386SLC. The 486SLC2 adds support for Intel's486 instruction set while still possessing the same 16-bit external data bus as the 386SLC. The Model 57 486SLC2 is otherwise identical to the Model 57 SX in terms of its chassis, number of expansion slots, and maximum RAM.^[34][35][36] Simultaneous with this announcement, IBM announced a successor to the Ultimedia M57 SLC, thePS/2 Ultimedia M57 486SLC2, featuring the same IBM 486SLC2 processor as the Model 57 486SLC2.^[36] Customers were able to upgrade the 57 SX to the 57 486SLC2 with a drop-in processor upgrade kit.^[36] The PS/2 Model 57 486SLC2 was among the first products of the newly formedIBM Personal Computer Company (IBM PC Co.), an autonomous subsidiary of IBM created earlier in the month.^[35] IBM followed up this model with thePS/2 Model 57 486SLC3 in February 1994. It featured a 16-bit variant of their 32-bit"Blue Lightning" IBM 486BL chip, clocked at 75 MHz. The Model 57 486SLC3 was otherwise identical to its predecessor, down to the case and expansion slots. Like its predecessor, Model 57 486SLC2 could be upgraded to the Model 57 486SLC3 with a drop-in upgrade kit.^[37]

The PS/2 Model 56 is the direct successor the Model 55 SX. Introduced by IBM in February 1992, it originally came in two variants: thePS/2 Model 56 SX, featuring a 20-MHz 386SX processor; and thePS/2 Model 56 SLC, featuringIBM's 386SLC processor, also clocked at 20 MHz.^[48][49] Despite being based on Intel's 386SX, IBM's 386SLC performed better in multiplebenchmarks on account of the presence ofL1 cache that Intel's 386SX lacks; per other benchmarks, the 386SLC even boasted superior performance than Intel's cacheful 25-MHz 386 processor.^[48][50] Both the Model 56 SX and the Model 56 SLC feature three 16-bit Micro Channel architecture slots, VGA graphics, and 4 MB of RAM stock, expandable to 16 MB.^[48][49] Customers were able to upgrade the 56 SX to the 56 SLC with a drop-in processor upgrade kit.^[50] Both models were available in diskless workstation variants—thePS/2 Model 56 LS and thePS/2 Model 56 SLC LS—with either a Token Ring or an Ethernet adapter.^[49]

In September 1992, IBM introduced thePS/2 Model 56 486SLC2, featuring the 50-MHzIBM 486SLC2 processor. The Model 56 486SLC2 sports the same case and three MCA expansion slots as its predecessor; like the Model 56 SX before it, customers could upgrade the 56 SLC to the 56 486SLC2 with a drop-in processor upgrade kit.^[35] Along with the Model 57 486SLC2, the Model 56 486SLC2 was among the first products of IBM PC Co.^[35] IBM followed up this model with thePS/2 Model 56 486SLC3 in February 1994, featuring IBM's 75 MHz Blue Lightning chip. The Model 56 486SLC3 was otherwise identical to its predecessor, down to the case and expansion slots. Unlike the Model 56 486SLC2, the Model 56 486SLC3 came in a diskless workstation variant, thePS/2 Model 56 486SLC3 LS, equipped with either a Token Ring or an Ethernet adapter.^[51][29]

The PS/2 Model 53 486SLC2 was introduced by IBM in November 1993 as the company's new lowest-end model in the PS/2 lineup.^[28] It features the 50-MHz IBM 486SLC2 processor, between 4 MB and 16 MB of RAM, and either a 120-MB or a 250-MB hard drive. IBM also offered a diskless workstation variant branded as thePS/2 Model 53 LS, with either a Token Ring or an Ethernet adapter.^[20] Like the Model 55 SX, the Model 53 486SLC2 features three 16-bit Micro Channel slots and VGA graphics.^[28]

IBM outsourced the design of the Model 53 486SLC2 in large part to Reply Corporation, a major vendor of aftermarket upgrade products for the PS/2.^[58] Reply largely borrowed wholesale the case design of the Model 55 SX for the Model 53 486SLC2, unlike the Model 56 and Model 57, which were ground-up redesigns. The Model 53 486SLC2's motherboard was originally marketed by Reply as a standalone upgrade motherboard called the PS/2 Model 55SX TurboProcessor, released earlier in February 1993.^[59][60]

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