diff --git a/Components/DiskII/IWM.cpp b/Components/DiskII/IWM.cpp
index 5e2861911..385d53bdb 100644
--- a/Components/DiskII/IWM.cpp
+++ b/Components/DiskII/IWM.cpp
@@ -105,7 +105,7 @@ uint8_t IWM::read(int address) {
 				bit 7: 1 = write data buffer ready for data.
 			*/
 			LOG("Reading write handshake");
-		return 0x1f | 0x80 | 0x40;
+		return 0x1f | write_handshake_;
 	}
 
 	return 0xff;
@@ -143,7 +143,7 @@ void IWM::write(int address, uint8_t input) {
 		break;
 
 		case Q7|Q6|ENABLE:	// Write data register.
-			LOG("Data register write\n");
+			LOG("Data register write");
 		break;
 	}
 }
@@ -233,24 +233,34 @@ void IWM::run_for(const Cycles cycles) {
 //	}
 
 	// Activity otherwise depends on mode and motor state.
-	const bool run_disk = drives_[active_drive_];	// drive_motor_on_ &&
 	int integer_cycles = cycles.as_int();
 	switch(state_ & (Q6 | Q7 | ENABLE)) {
 		case 0:
 		case ENABLE:	// i.e. read mode.
-			while(integer_cycles--) {
-				if(run_disk) {
+			if(drive_is_rotating_[active_drive_]) {
+				while(integer_cycles--) {
 					drives_[active_drive_]->run_for(Cycles(1));
+					++cycles_since_shift_;
+					if(cycles_since_shift_ == bit_length_ + Cycles(2)) {
+						propose_shift(0);
+					}
 				}
-				++cycles_since_shift_;
-				if(cycles_since_shift_ == bit_length_ + Cycles(2)) {
+			} else {
+				while(cycles_since_shift_ + integer_cycles >= bit_length_ + Cycles(2)) {
 					propose_shift(0);
+					integer_cycles -= bit_length_.as_int() + 2 - cycles_since_shift_.as_int();
 				}
+				cycles_since_shift_ += Cycles(integer_cycles);
 			}
 		break;
 
+		case Q6|Q7:
+		case Q6|Q7|ENABLE:	// write mode?
+			printf("IWM write mode?\n");
+		break;
+
 		default:
-			if(run_disk) drives_[active_drive_]->run_for(cycles);
+			if(drive_is_rotating_[active_drive_]) drives_[active_drive_]->run_for(cycles);
 		break;
 	}
 }
@@ -278,4 +288,15 @@ void IWM::propose_shift(uint8_t bit) {
 void IWM::set_drive(int slot, IWMDrive *drive) {
 	drives_[slot] = drive;
 	drive->set_event_delegate(this);
+	drive->set_clocking_hint_observer(this);
+}
+
+void IWM::set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) {
+	const bool is_rotating = clocking != ClockingHint::Preference::None;
+
+	if(component == static_cast<ClockingHint::Source *>(drives_[0])) {
+		drive_is_rotating_[0] = is_rotating;
+	} else {
+		drive_is_rotating_[1] = is_rotating;
+	}
 }
diff --git a/Components/DiskII/IWM.hpp b/Components/DiskII/IWM.hpp
index b26fe142c..c9dee5219 100644
--- a/Components/DiskII/IWM.hpp
+++ b/Components/DiskII/IWM.hpp
@@ -10,6 +10,7 @@
 #define IWM_hpp
 
 #include "../../ClockReceiver/ClockReceiver.hpp"
+#include "../../ClockReceiver/ClockingHintSource.hpp"
 #include "../../Storage/Disk/Drive.hpp"
 
 #include <cstdint>
@@ -37,11 +38,11 @@ struct IWMDrive: public Storage::Disk::Drive {
 	virtual void set_enabled(bool) = 0;
 	virtual void set_control_lines(int) = 0;
 	virtual bool read() = 0;
-	virtual void write(bool value) = 0;
 };
 
 class IWM:
-	public Storage::Disk::Drive::EventDelegate {
+	public Storage::Disk::Drive::EventDelegate,
+	public ClockingHint::Observer {
 	public:
 		IWM(int clock_rate);
 
@@ -81,8 +82,12 @@ class IWM:
 
 		int active_drive_ = 0;
 		IWMDrive *drives_[2] = {nullptr, nullptr};
+		bool drive_is_rotating_[2] = {false, false};
+
+		void set_component_prefers_clocking(ClockingHint::Source *component, ClockingHint::Preference clocking) override;
 
 		Cycles cycles_until_motor_off_;
+		uint8_t write_handshake_ = 0xc0;
 
 		void access(int address);
 
diff --git a/Components/DiskII/MacintoshDoubleDensityDrive.cpp b/Components/DiskII/MacintoshDoubleDensityDrive.cpp
index c47399503..7db79c2bc 100644
--- a/Components/DiskII/MacintoshDoubleDensityDrive.cpp
+++ b/Components/DiskII/MacintoshDoubleDensityDrive.cpp
@@ -8,6 +8,14 @@
 
 #include "MacintoshDoubleDensityDrive.hpp"
 
+/*
+	Sources used pervasively:
+
+	http://members.iinet.net.au/~kalandi/apple/AUG/1991/11%20NOV.DEC/DISK.STUFF.html
+	Apple Guide to the Macintosh Family Hardware
+	Inside Macintosh III
+*/
+
 using namespace Apple::Macintosh;
 
 DoubleDensityDrive::DoubleDensityDrive(int input_clock_rate, bool is_800k) :
@@ -65,27 +73,27 @@ void DoubleDensityDrive::set_control_lines(int lines) {
 	if((old_state ^ control_state_) & control_state_ & Line::LSTRB) {
 		switch(control_state_ & (Line::CA1 | Line::CA0 | Line::SEL)) {
 			default:
-//				LOG("Unhandled LSTRB");
 			break;
 
-			case 0:
-//				LOG("LSTRB Set stepping direction: " << int(state_ & CA2));
+			case 0:						// Set step direction — CA2 set => step outward.
 				step_direction_ = (control_state_ & Line::CA2) ? -1 : 1;
 			break;
 
-			case Line::CA1:
-//				LOG("LSTRB Motor");
+			case Line::CA1:				// Set drive motor — CA2 set => motor off.
 				set_motor_on(!(control_state_ & Line::CA2));
 			break;
 
-			case Line::CA0:
-//				LOG("LSTRB Step");
-				step(Storage::Disk::HeadPosition(step_direction_));
+			case Line::CA0:				// Initiate a step, if CA2 is clear.
+				if(!(control_state_ & Line::CA2))
+					step(Storage::Disk::HeadPosition(step_direction_));
 			break;
 
-			case Line::CA1 | Line::CA0:
-//				LOG("LSTRB Eject disk");
-				set_disk(nullptr);
+			case Line::SEL:				// Reset has-been-ejected flag (if CA2 is set?)
+			break;
+
+			case Line::CA1 | Line::CA0:	// Eject the disk if CA2 is set.
+				if(control_state_ & Line::CA2)
+					set_disk(nullptr);	// TODO: should probably trigger the disk has been ejected bit?
 			break;
 		}
 	}
@@ -94,75 +102,64 @@ void DoubleDensityDrive::set_control_lines(int lines) {
 bool DoubleDensityDrive::read() {
 	switch(control_state_ & (CA2 | CA1 | CA0 | SEL)) {
 		default:
-//			LOG("unknown)");
 		return false;
 
-		// Possible other meanings:
-		// B = ready			(0 = ready)
-		// C = disk switched?
-		//
-		// {CA1,CA0,SEL,CA2}
-
 		case 0:					// Head step direction.
 								// (0 = inward)
-//			LOG("head step direction)");
 		return step_direction_ <= 0;
 
 		case SEL:				// Disk in place.
 								// (0 = disk present)
-//			LOG("disk in place)");
 		return !has_disk();
 
 		case CA0:				// Disk head step completed.
 								// (0 = still stepping)
-//			LOG("head stepping)");
 		return true;	// TODO: stepping delay. But at the main Drive level.
 
 		case CA0|SEL:			// Disk locked.
 								// (0 = write protected)
-//			LOG("disk locked)");
 		return !get_is_read_only();
 
 		case CA1:				// Disk motor running.
 								// (0 = motor on)
-//			LOG("disk motor running)");
 		return !get_motor_on();
 
 		case CA1|SEL:			// Head at track 0.
 								// (0 = at track 0)
-//			LOG("head at track 0)");
+								// "This bit becomes valid beginning 12 msec after the step that places the head at track 0."
 		return !get_is_track_zero();
 
+		case CA1|CA0:			// Disk has been ejected.
+								// (0 = user has ejected disk)
+		return false;
+
 		case CA1|CA0|SEL:		// Tachometer.
 								// (arbitrary)
 		return get_tachometer();
 
 		case CA2:				// Read data, lower head.
-//			LOG("data, lower head)\n");
 			set_head(0);
-		return false;;
+		return false;
 
 		case CA2|SEL:			// Read data, upper head.
-//			LOG("data, upper head)\n");
 			set_head(1);
 		return false;
 
 		case CA2|CA1:			// Single- or double-sided drive.
 								// (0 = single sided)
-//			LOG("single- or double-sided drive)");
 		return get_head_count() != 1;
 
 		case CA2|CA1|CA0:		// "Present/HD" (per the Mac Plus ROM)
 								// (0 = ??HD??)
-//			LOG("present/HD)");
+								//
+								// Alternative explanation: "Disk ready for reading?"
+								// (0 = ready)
 		return false;
 
 		case CA2|CA1|CA0|SEL:	// Drive installed.
 								// (0 = present, 1 = missing)
-//			LOG("drive installed)");
+								//
+								// TODO: why do I need to return this the wrong way around for the Mac Plus?
 		return true;
 	}
 }
-
-void DoubleDensityDrive::write(bool value) {
-}
diff --git a/Components/DiskII/MacintoshDoubleDensityDrive.hpp b/Components/DiskII/MacintoshDoubleDensityDrive.hpp
index 7e070b7db..00665dcae 100644
--- a/Components/DiskII/MacintoshDoubleDensityDrive.hpp
+++ b/Components/DiskII/MacintoshDoubleDensityDrive.hpp
@@ -21,7 +21,6 @@ class DoubleDensityDrive: public IWMDrive {
 		void set_enabled(bool) override;
 		void set_control_lines(int) override;
 		bool read() override;
-		void write(bool value) override;
 
 	private:
 		// To receive the proper notifications from Storage::Disk::Drive.