The Spectrum was the realisation of Sir Clive Sinclair's dream of an affordable home computer. A cheap and cheerful home computer with fairly simple hardware, around at the same time as the BBC and C64, cheaper than both the others, and still expandable with various peripherals, it became very popular with home users. For many people the Spectrum was their first computer, and it's perhaps for that reason that so many emulators for it have sprung up.
The first spectrum emulator on the Acorn was called the Speculator, or Speccy, with the last release of the emulator in October 1990. The emulator is implemented as a module, and works off the desktop, emulating a 48Kb Spectrum. It was perculiar in that instead of using the standard Z80 and SNA files for images and snapshots, it invented its own speculator formats (unused by anything else). Luckily Mike Perigo has added a few utilities to the archive, to convert between formats, as well as a simple Z80 disassembler. Unfortunately I believe that the emulator is not RISC OS 3 compatible, and will probably therefore not work on most Acorns, I would be happy to be proved wrong though.
Speed Rating:
ARM 2 
ARM 3
StrongARM 
Requires RISC OS 2
The best freeware spectrum emulator is the MZX spectrum emulator written
for the Acorn by 'ARM unlimited', otherwise known as Graham Willmott (no
valid email address). It emulates most of the functionality of a 48Kb Sinclair
ZX Spectrum. Needs at least 1Mb of memory and RISC OS 3 or later. Can even
run multitasking as well as singletasking although is a little jerky doing
this on my A5000.
Apparently 100% emulation speed is even possible on an ARM 2 machine now, though it won't run on Risc OS 2, as it is optimised for RiscPC 600. Sound support is only limited, although some sounds are recognisable. It is estimated to run 98% of snapshots without any problems. Although the docs report that this emulator is still under development, it has not altered since April 1994.
Apparently there is some sort of simple bug fix needed for MZX to work, details are available below, though I had no problem running it myself. On the RISC PC however, The ARM Club's Game on software is required if you want it to run.
Speed Rating: ARM
3 
StrongARM
MZX v1.1 (86Kb)
Spark archive
MZX bug fix
Spec128 by Joe
Kelleher is the first freeware Spectrum emulator to have 128K as well as
48K support. It is still in development, but if you want a copy Joe will
send you one. The compatibility of this ARM coded emulator is supposed
to be very good, and sound emulation is also very crisp. The Z80 emulator
used is based on that found in a CP/M emulator by David Higton (used with
permission) to make life a bit easier. This single-tasking emulator looks
like being a cheap alternative to Z80Em, and if all goes well may even
replace it. Eventually Joe is hoping to add emulation of the Plus D disk
drive interface and the Multiface 128, as well as support for all saved
states and tape dump formats and possibly a multi-tasking mode. At the
moment Joe is having a few problems with 32Kb page Acorns, since he is
doing true page mapping on the Acorn, rather than fudging it, which might
not be fixed for the first release, we'll just have to wait and see.
Speed Rating:
ARM 3
ARM 6
StrongARM
There is also a commercial Z80Em, supplied by Warm Silence Software, costing £15+VAT, current version is 2.1. 128K support is now available, as is full sound emulation. A demo version is available to download, which also appeared on the February 1996 disk 2 of Archimedes World. This is by far the best Spectrum emulator available, with nigh on perfect emulation, but your usage may not justify the price.
WSS also provide Speccie Emulator '96 CD full of old Spectrum games that can be run under either emulator, emulators for PC, Mac and Amiga and also scanned posters and covers of several games. It makes a good alternative to trawling through the pages listed below, and costs £18+VAT.
Speed Rating: ARM
3
Z80Em
demo (from WSS)
Z80Em
online manual
Warm Silence Software
(WSS) Z80Em page
SPConv
There ahve been several different file formats developed for Spectrum images over the years, but none has really taken over as the definitive format. For this reason, different emulators support different formats which are hard to interchange, unless you have SPConv which can convert between all the main Spectrum formats.
There is also a Spectrum emulator written in Java available.
Technical Details
CPU - Z80 running at 3.5 MHz
RAM - 48K - 128K, (of which video RAM is fixed at 256*192/8
+ 32*24 bytes)
ROM - 16K
Sound - AY-3-8912 chip, 3 tone channels and 1 noise channel.
1-bit digital channel also provided for compatibility with 48k models of
Spectrum.
Display - No hardware sprites. Screensize: 32*24 chars or
256*192 pixels. Colours: 15 (or 16 if you assume that black and dark black
are different :) BUT you can only have 2 colours appearing in any given
character square (8 by 8 pixels)
reference - Michael Borcherds, author of Z80em & Joe Kelleher,
author of Spec128
Software:
Planet
Sinclair - loads of speccie info, emulators and software.
ftp://ftp.nvg.unit.no/pub/spectrum/
- ftp archive of lots of spectrum stuff
ftp://ftp.ijs.si/pub/zx/
- another ftp with loads of spectrum stuff
Snapshot database
- a massive database to search for snapshot images.
The Jasper page
has some images
World
of Spectrum
