As well as active and passive systems, RFID systems can also be broken out into different frequencies.
Some frequencies and systems are designed to only read one tag at a time, while others can read multiple. Cost of readers can also vary wildly based the frequency rating of the modules. In prior years a reader capable of reading multiple tags was in the thousands of dollars, sometimes tens of thousands. These systems were unattainable for most hobbyists and prototypers. However, this is finally beginning to change, and multi-read capable readers are becoming much more affordable.
Check out the following chart for a basic break down of the frequencies, and their associated properties.
|A Few Common RFID Reader Types|
|Frequency||AKA||Range||Read/Write||Read Multiple Tags Simultaneously||Average Tag Cost|
|Low Frequency (120-150 kHz)||"Chips/microchips" (in veterinary applications), prox cards, HID cards (both trade names)||Up to 20 cm/ < 1 foot||Read Only||No||$0.50|
|High Frequency (13.56 MHz)||MiFare, NFC||Up to 1 meter||Read/write||No||$1|
|Ultra High Frequency (433 MHz, 860-920 MHz)||Long-range RFID, powered RFID||Up to 100 meters||Read/write||Yes||$0.05|
|Information from Wikipedia: Radio-frequency identification|