Reel to reel machines fall into two categories, domestic and professional
Are usually designed for light work of a few hours a week and as such are mainly made from pressed steel panels and lots of springs and levers. Some better quality machines such as Revox and some Teac and Pioneer models use solenoid control of the various parts of the deck to reduce the risk of mechanical problems and improve reliability. Most domestic tape decks are of the two head variety, one erase the other combined record play. Head configurations for domestic recorders are 1/2 track mono on 1/4 inch tape, where you record one side then flip the tape over and record on the other side as well doubling the tape record time. Stereo models are 1/4 track two one way and another two when you turn over the tape. These are known as 1/4 track machines and will replay pre-recorded reel to reel tapes.
Most pre-recorded tapes are recorded at tape speeds of 3 3/4 ips or 7 1/2 ips (inches per second) the 3 3/4 ips tapes are usually 5:" spools the 7 1/2 ips better quality on 7" spools. Not all domestic recorders have capacity for 7" spools lower cost units only will take 5" ones.
Domestic recorders come in a variety of speeds that include 15/16, 1 7/8, 3 3/4, 7 1/2 ips, one or many speeds may be available
the more the better. Domestic recorders usually range in price from $50 to $250
Are usually designed for heavy duty work of 8 hours a day and as such are usually made from a cast aluminium frame, high grade motors and bearings and use solenoid control of the various parts of the deck to reduce the risk of mechanical problems and improve reliability. Most professional tape decks are of the three head variety, one erase one for record and a third for play. This allows direct monitoring off tape of what is being recorded for quality control. Studio's usually listen off tape in case of dropouts or other recording defects are detected. That way you can always go back and record again.
Head configurations are full track mono on 1/4 inch tape, where you record one side only. Stereo models are 1/2 track, two one way only if you flip the tape over the track plays in reverse. These are known as 1/2 track machines and will replay studio or broadcast recorded reel to reel tapes only, playing a domestic pre-recorded tape will result in hearing both forward and reverse tracks at the same time .
Most professional recorders have the capability to play up to 10" NAB tape spools, the exception are the BYER,ROLA, PLESSEY radio station broadcast recorders which mainly have 7" spool size capability (they did make other models such as the 33B, and Plessey 700 series which supported 10" NAB or external spooling adapters for the 7" machines)
Studio recorders come in a variety of speeds that include 15/16, 1 7/8, 3 3/4, 7 1/2, 15, 30 ips usually one or many speeds may be available the more the better. The most common speed combination is 7 1/2 ips and 15 ips. Professional machines usually start at $350 for commonly available ROLA Machines and upwards to more than $60,000 for a Studer C37