IN­SIDE IBM PC 5150

PC Advisor - - CONTENTS -

The first IBM PC

Thirty five years ago, in Au­gust 1981, IBM launched the most in­flu­en­tial com­mer­cial com­puter sys­tem of all time, the IBM PC 5150. Over the past three and a half decades, ar­chi­tec­tural de­scen­dants of this sin­gle ma­chine have taken over the desk­top, work­sta­tion, server and even game con­sole mar­kets. And de­spite in­roads from ARMbased smart­phones, its dig­i­tal de­scen­dants are still re­lied upon for just about all the heavy lift­ing in the com­puter in­dus­try.

On the an­niver­sary of such a mon­u­men­tally im­por­tant com­puter, we thought it would be in­struc­tive to take a deeper look into the ma­chine that started it all. How? By tak­ing apart one of these bad boys on my trusty work­bench, of course. And that’s ex­actly what you’ll see in the im­ages ahead.

IBM’s CGA dis­play

Be­fore we take apart the IBM PC, we’d like to point out a few pe­riph­eral com­po­nents that come to­gether to form a com­plete IBM PC sys­tem. The most ob­vi­ous com­po­nent is the mon­i­tor. Many screens were avail­able for the IBM PC in the years fol­low­ing its re­lease, in­clud­ing an IBM brand mono­chrome unit and the IBM CGA mon­i­tor you see here (on which we’re play­ing the share­ware clas­sic ZZT). This mon­i­tor re­quired the op­tional pur­chase of a CGA video card. In its stan­dard 320x200 graph­ics mode, the CGA could dis­play only four colours at a time from a pal­ette of 16. In this case, ZZT uses text-mode graph­ics, so it can dis­play any of the 16 colours at once.

The first IBM PC key­board

The first IBM PC key­board, seen here, bor­rowed heav­ily from the in­dus­trial-strength IBM Sys­tem/23 Data­mas­ter com­puter which pre­ceded it. The key­board is hefty (around 2.7kg), loud and clicky, and its lay­out was slightly un­usual at the time of its launch. (It wouldn’t be un­til the Model M key­board in 1984 that the stan­dard 101-key lay­out we all know and use to­day would be fi­nalised.)

De­spite its awk­ward lay­out, this first PC key­board won high praise from crit­ics for its pre­ci­sion and dura­bil­ity. You could knock some­one stone cold un­con­scious with it and it would still work. In the 1980s, we used to test com­put­ers that way.

Crack­ing the case

The only things sep­a­rat­ing us from the in­side of an IBM PC were five pre­ci­sion flat­head IBM screws, which came out eas­ily. The heavy gauge sheet metal case slides off with no trou­ble, ex­pos­ing the ma­chine’s in­sides.

You can’t see it too clearly in this photo, but we al­ways like to point out that the IBM PC first shipped with a cas­sette drive port (right next to the key­board port), which al­lowed users with­out floppy drives to save their IBM BA­SIC pro­grams to an au­dio cas­sette tape. In 1981, floppy drives were an ex­pen­sive op­tion, so IBM cov­ered ev­ery pos­si­ble mar­ket seg­ment with cus­tom build op­tions – from bare-bones to decked-out.

Benj Ed­wards rewinds the clock by 35 years and re­vis­its one of the PCs that started it all

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