This schematic shows several ATtiny25 minimal circuit configurations. The ATtiny25 is shown using its internal 8 MHz RC oscillator, which divided by 8 gives a 1 MHz system clock, and with an external crystal. The ATtiny25 has 2kB flash, 128 bytes of SRAM, and 128 bytes of EEPROM. There are two 8-bit timers, and no 16-bit timers.
Here you can find the current ATtiny25 datasheet