Sinclair ZX-81


Owner of the one pictured: Edward Hammond
Donor of Tom's: James (Jimbo) Manfield
Location: unknown


I finally managed to luck into one of these, direct from England. Mine as an added chiclet keyboard that looks great. There are new pictures below, but they didn't turn out very sharp.


Edward Hammond Comments:

As I recall, I got this computer when I was 12. That would make it 1980. Does that sound right? It was my first, and it was a little intimidating at the start. Although I eventually learned how to do OK with the ZX-81 BASIC, I initially limited myself to "annoy-your-siblings" programs. It went sort of like this:

10 FOR X=1 TO 500
20 PRINT "Elizabeth is a Lizardbreath"
30 NEXT X

About the time I started to get really good at this and delve into the expanded capability of the 16k RAM module (the ZX-81 has only 1k of on-board RAM), I was distracted by high school, Apple II's and later Macs. Now, I mainly work on a PPC 8500/120.

Technical Specifications: (taken directly from the Operating Supplement)

  • Depth: 167 mm (6.32 in)
  • Height: 40 mm (1.57 in)
  • Weight: 350 grams (12.15 oz)
  • CPU: Z80Z at 3.25 MHz
  • ROM: Containing 8k BASIC interpreter
  • RAM: 1K byte internal, externally expandable to 16K bytes

Other Spec's (summarized from Supplement):

Keyboard:
40 key, w/ graphics and function modes, includes 20 graphical and 54 inverse video characters Sinclair calls the keyboard a "touch sensitive membrane".
Display:
24 lines x 32 characters (text)
64 x 44 pixels in graphics mode
Modes:
FAST and SLOW modes. In SLOW mode, "the ZX81 will both compute and display simultaneously." In FAST mode, you go 4 times faster, but the display is delayed and jerky.
Storage:
"Programs and data can be saved onto the cassette [not provided] so that they are not lost when the ZX81 is turned off." Transfer rate to and from the cassette recorder is 250 baud.
Floating Point:
"Numbers are stored in 5 bytes in floating-point binary form... accurate to 9 1/2 decimal digits"
Power:
Requires 420ma at 7-11V DC. This is the only piece of the original package I have lost.

Pictures:


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